Polymer free-radically prepared

Note Polymers were free radically prepared using 2,2 -azobisisobutyronitrile. 

Viscosity data for three linear polymers corrected to the friction coefficient of high molar mass polymer at roughly 7 g+ 120K, fit to Eq. (8.137) (curves). Open circles are polyisobutylene (r=50°C) with Mc = 14000 gmoP. filled squares are polybutadiene (7 =25°C) with A/< = 6700gmor open triangles are free radically prepared polystyrene T =217°C), and filled triangles are anionically prepared polystyrene T=2[1 C) with... 

All free radical prepared polymers are believed to incorporate enamine structures or ketonitrile if the polymerization conditions favored hydrolysis. The rate of yellowing of PAN in air at low temperatures is proportional to the concentration of the above defects. 

A/ -Vinylformamide (NVF), a reactive functional monomer with novel physical and chemical properties and favorable toxicology (1,2) has shown significant promise in a number of application areas. It is highly reactive under free radical or cationic reaction conditions. The free radically prepared homopolymer is readily water soluble and can be hydrolyzed in a controllable fashion to give cationic or free base amine functional polymers. NVF, like other vinylamides, also copolymerizes well with most commercially available monomers, especially vinyl acetate, acrylamides, and acrylates (2). NVF s moderate toxicity enables the material to be used in applications where there is some possibility of worker exposure. However, it is difficult to obtain with NVF alone the broad range of physical and chemical properties needed for many applications requiring different glass transition temperatures and variable hydrophilic and hydrophobic characteristics. Also, there are situations where the toxicity profile of the monomer system is a primary concern and NVF may not be considered adequately safe. 

Of all the MA copolymerizations studied, the MA-styrene pair has perhaps received the greatest attention in an attempt to understand the mechanism of alternating copolymerization.For this pair, the understanding is complicated by the fact that styrene-rich copolymers can be prepared from styrene-rich feeds. Bamford and Barb studied the copolymerization of the styrene-MA pair in several solvents and Barb interpreted the kinetics of the reaction in terms of a penultimate group (i.e., unit adjacent to the radical end group) effect operating on polymer free radicals with a terminal styrene unit. Enomoto et after studying the same reaction... 

Allyl group containing polymers have been found to cross-link readily on e-beam exposure. Free radical solution polymerization of allyl methacrylate has been shown to result in a unique polymer with about 65% pendant allyl groups and the remainder believed to be involved in a cyclization propagation step. The exact structure of this polymer has yet to be established however, it differs significantly in physical properties from anionically prepared poly(allyl methacrylate), which has a structure with 100% pendant allyl groups. The of the former polymer is llO C, compared to the latter, which is 36 The free radically prepared polymer is very sensitive to e-beam radiation (1.5 X 10"Ccm" at lOkeV) but has poor physical properties such as adhesion, etc. Copolymerization of allyl methacrylate with glycidyl methacrylate results in copolymers with equivalent... 

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

The elastomer produced in greatest amount is styrene-butadiene rubber (SBR) Annually just under 10 lb of SBR IS produced in the United States and al most all of it IS used in automobile tires As its name suggests SBR is prepared from styrene and 1 3 buta diene It is an example of a copolymer a polymer as sembled from two or more different monomers Free radical polymerization of a mixture of styrene and 1 3 butadiene gives SBR... 

Section 1117 Polystyrene is a widely used vinyl polymer prepared by the free radical polymerization of styrene... 

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

Remember from Sec. 1.3 that graft copolymers have polymeric side chains which differ in the nature of the repeat unit from the backbone. These can be prepared by introducing a prepolymerized sample of the backbone polymer into a reactive mixture—i.e., one containing a source of free radicals—of the side-chain monomer. As an example, consider introducing polybutadiene into a reactive mixture of styrene ... 

Figure 6.11 Comparison of the number distribution of n-mers for polymers prepared from anionic and free-radical active centers, both with f = 50.

In some instances, the resist polymer can be prepared in a single step by direct polymerization of the protected monomer(s) (37,88), entirely avoiding the intermediate PHOST. HOST-containing resist polymers have also been prepared by free-radical copolymerization of a latent HOST and a stable, acid-labile monomer, eg, the copolymerization of acetoxystyrene with tert-huty acrylate, followed by selective removal of the acetoxy group (89) (Fig. 30). 

Poly(acrylic acid) and Poly(methacrylic acid). Poly(acryHc acid) (8) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (36) (with cross-linker for superadsorber appHcations) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78° C provides a syndiotactic form (37) that can be hydrolyzed to syndiotactic PAA. From academic studies, alkaline hydrolysis of the methyl ester requires a lower time than acid hydrolysis of the polymeric ester, and can lead to oxidative degradation of the polymer (38). Po1y(meth acrylic acid) (PMAA) (9) is prepared only by the direct polymerization of the acid monomer it is not readily obtained by the hydrolysis of methyl methacrylate. 

Other fairly recent commercial products, poly(vinyl amine) and poly(vinyl amine vinyl alcohol), have addressed the need for primary amines and their selective reactivity. Prior efforts to synthesize poly(vinyl amine) have been limited because of the difficulty hydrolyzing the intermediate polymers. The current product is prepared from /V-ethenylformamide (20) formed from the reaction of acetaldehyde and formamide. The vinyl amide is polymerized with a free-radical initiator, then hydrolyzed (eq. 7). 

The cyanoacryhc esters are prepared via the Knoevenagel condensation reaction (5), in which the corresponding alkyl cyanoacetate reacts with formaldehyde in the presence of a basic catalyst to form a low molecular weight polymer. The polymer slurry is acidified and the water is removed. Subsequendy, the polymer is cracked and redistilled at a high temperature onto a suitable stabilizer combination to prevent premature repolymerization. Strong protonic or Lewis acids are normally used in combination with small amounts of a free-radical stabilizer. 

Uses. About 35% of the isophthahc acid is used to prepare unsaturated polyester resins. These are condensation products of isophthahc acid, an unsaturated dibasic acid, most likely maleic anhydride, and a glycol such as propylene glycol. The polymer is dissolved in an inhibited vinyl monomer, usually styrene with a quinone inhibitor. When this viscous hquid is treated with a catalyst, heat or free-radical initiation causes cross-linking and sohdification. A range of properties is possible depending on the reactants used and their ratios (97). 

In tbe first attempt to prepare a two-dimensional crystalline polymer (45), Co y-radiation was used to initiate polymerization in monolayers of vinyl stearate (7). Polymerization at the air—water interface was possible but gave a rigid film. The monomeric monolayer was deposited to give X-type layers that could be polymerized in situ This polymerization reaction, quenched by oxygen, proceeds via a free-radical mechanism. 

Polymers ndResins. / fZ-Butyl peroxyneopentanoate and other peroxyesters of neopentanoic acid can be used as free-radical initiators for the polymeri2ation of vinyl chloride [75-01-4] (38) or of ethylene [74-85-1]. These peresters have also been used in the preparation of ethylene—vinyl acetate copolymers [24937-78-8] (39), modified polyester granules (40), graft polymers of arninoalkyl acrylates with vinyl chloride resins (41), and copolymers of A/-vinyl-pyrrohdinone [88-12-0] and vinyl acetate [108-05-4] (42). They can also be used as curing agents for unsaturated polyesters (43). 

Polybutadiene was first prepared in the early years of the 20th century by such methods as sodium-catalysed polymerisation of butadiene. However, the polymers produced by these methods and also by the later free-radical emulsion polymerisation techniques did not possess the properties which made them desirable rubbers. With the development of the Ziegler-Natta catalyst systems in the 1950s, it was possible to produce polymers with a controlled stereo regularity, some of which had useful properties as elastomers. 

It has not been found possible to prepare high polymers from a-methylstyrene by free-radical methods and ionic catalysts are used. The reaction may be carried out at about -60°C in solution. 

Polystyrene produced by free-radical polymerisation techniques is part syndio-tactic and part atactic in structure and therefore amorphous. In 1955 Natta and his co-workers reported the preparation of substantially isotactic polystyrene using aluminium alkyl-titanium halide catalyst complexes. Similar systems were also patented by Ziegler at about the same time. The use of n-butyl-lithium as a catalyst has been described. Whereas at room temperature atactic polymers are produced, polymerisation at -30°C leads to isotactic polymer, with a narrow molecular weight distribution. 

Free radicals are initially generated whenever polymer chains are broken and carbon radicals are formed. These effects occur during manufacture and in service life. Many elastomers are observed to oxidize at relatively low temperature (about 60°C), where carbon-hydrogen and carbon-carbon bond cleavages are highly unlikely. It has been demonstrated [52] that traces of peroxides impurities in the rubber cause low-temperature oxidation of rubber. These initiating peroxides are present in even the most carefully prepared raw rubber polymer [53]. 

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