Comonomers random incorporation

We use carbon-13 NMR spectrometry to identify the monomer units present in copolymers, their absolute concentrations, the probability that two or more monomer units occur in proximity, and long chain branching concentrations. For instance, in the case of polyethylene, we can not only distinguish and quantify ethyl, butyl, and hexyl branches, but we can also determine whether branches are present on carbon backbone atoms separated by up to four bonds. We can compare the observed adjacency of branches to a theoretical value calculated for random comonomer incorporation. By this method, we can determine whether comonomers are incorporated at random, as blocks, or in some intermediate fashion. 

As a result of the catalyst and process conditions used in their manufacture, the particular copolymers of current major interest are atactic, and contain typically up to about 50 mol% ( 80 wt%) styrene. These materials have been described as pseudo-random , since successive head-to-tail styrene chain insertions have been shown to be absent, even at high levels of styrene incorporation [1,2]. The term ethylene-styrene interpolymer (ESI) is used here to describe the specific ethylene-styrene copolymers produced via INSITE Technology. For convenience, all subsequent comonomer contents are expressed in weight percentages, unless otherwise stated. For example, the code ES70 refers to an interpolymer having 70 wt.% comonomer styrene incorporation. 

The main feature of polymers is their MMD, which is well known and understood today. However, several other properties in which the breadth of distribution are important and influence polymer behavior (see Figure 1) include physical, the classical chain-length distribution chemical, two or more comonomers are incorporated in different fractions topological, polymer architecture may differ (e.g., linear, branched, grafted, cyclic, star or comb-like, and dendritic) structural, comonomer placement may be random, block, alternating, and so on and functional, distribution of chain functions (e.g., all chain ends or only some carry specific groups). Other properties the polymers may disperse (tacticity and crystallite dimensions) are not of the same general interest or cannot be characterized by solution methods. 

It is also possible to copolymerize ethylene with a-olefins such as propene, 1-butene, 1-pentene, 1-hexene, and 1-octene, forming linear low-density polyethylene (LLDPE). The product of copolymerization parameters V2 obtained by using ethylenebis(l-indenyl)zirconium dichloride (11) indicates random incorporation of the comonomer [38]. 

If DCPD is copolymerized with other NBE-type monomers like 2-norbornene-5-methylester (NBE-ME), using 4 as catalyst, the Tg of the so obtained copolymers decrease linearly with the NBE-ME content from 145°C (pure DCPD) to 57°C (pure NBE-ME) and the swelling in toluene increases from 100 to >900%, pointing to a sharp decrease in the crosslink density. This and similar experiments with other comonomers suggest a random incorporation of the comonomer into the poly(DCPD) network. 

The free radical polymerizations of 3-[(2-Acrylamido-2-mefliyl propyl)dimethylammonio]-l-propanesulfonate with acrylamide and/or acrylic acid, and 3-(i Tj -diallyl-i /-methylammonio)-l-propanesulfonate with A, iV diailyl-i, iV-dimethyl ammonium chloride or AT,A/-diallyl-iV,-methyl amine have been studied. Reactivity ratios indicate random incorporation of comonomers. Molecular weights range from 3.0 x 10 to 15.1 x 10 g mol for the acrylamido-based copolymers and from 2.2 x 10 to 6.0 x 10 g mol for the cyclocopolymers. Second virial coefficients and viscosities decrease as sulfobetaine content increa s for each of the copolymers. A transition from polyelectrolyte to polyampholyte behavior is observed with added NaCl for those copolymers with sulfobetaine monomer incorporation greater than 40 mol%... 

Sulfobetaine cydopolymers. The first sulfobetaine cyclopolymer series OGQ) consists of the copolymers of 6 with 8 (Scheme 6) (42,43). Compositional analysis of this series of cyclopolymers is listed in Table 3. Reactivity ratios, determined via nonlinear least squares analysis " of chemical compositions determined from gated-decoupled C NMR, indicate random incorporation of the comonomers (ri=1.14 r2=0.97). The five-membered ring structure common to polymerized diallyl ammonium salts was retained in the sulfobetaine mer unit. Weight average molecular weights for this series range from 3.04 x 10" to 6.03 x 10 g mol. Second virial coefficients decrease from 8.78 x 10"" to 2.50 x lO"" ml mol g as the amount of 8 incorporated into the copolymer increases. 

The NMR experiments were carried out not only to verily the reaction kinetics but also to estimate the reactivity of the two comonomers, by studying the copolymer composition. The most relevant information obtained by the authors from the NMR spectra is that the comonomers were incorporated equally into the copolymer chains, a random distribution being obtained, independent of the EO/IGG ratio and for all temperatures studied. C NMR analysis allowed to investigate the monomer triad sequence distribution and supported the authors conclusions on the random incorporation of the comonomers. 

Random or statistical copolymers can be prepared by one-pot ATRP of two monomers when there is essentially random incorporation of monomers into the copolymer. This type of copolymer is formed in radical copolymerization when the reactivity ratio of each comonomer is dose to unity.In ARGET ATRP, the lower concentration of catalyst results in less frequent aaivation/deactivation cydes and incorporation of more monomer units in each cyde, resulting in higher values of but this slightly longer period of intermittent... 

Randomly incorporated ethylene introduces defects along the backbone. These defects dismpt crystallization, reducing the modulus, melting point, and heat of fusion. The incorporation of random ethylene also reduces haze. Butene has also been used as a comonomer in PP. With the development of metallocene catalysts, even higher a-olefins such as hexene could be incorporated. While these alternative copolymers are now technically feasible, they have not seen commercial... 

The melting point of a polymer will also be affected by copolymerization. In the case of random or statistical copolymers (Section 1.2.3) the structure is very irregular and so crystallization is normally suppressed and the copolymers are usually amorphous. In contrast, in block and graft copolymers crystallization of one or more of the blocks may take place. It is possible to analyse the melting behaviour for a copolymer system in which there are a small number of non-crystallizable comonomer units incorporated in the chain, using Equation (4.39). These units will act as impurities (cf. chain ends) and so the melting point of the copolymer will be given by... 

Copolymers are macromolecules composed of two or more chemically distinct monomer units, covalently joined to form a common polymer chain [1,2], In these materials, the sequence distribution of the monomer counits plays a critical role in determining the copolymer s crystallization behavior, and consequently influences its solid-state morphology and material properties [1,2], At one extreme, different types of monomer units may be randomly incorporated into the polymer chain, resulting in a statistical copolymer. At the other extreme, blocks of homopolymer sequences of different chemical nature and chain length may be joined together to form what is known as a block copolymer. In this chapter, we wiU review the key effects of comonomer incorporation on the solid-state morphology and crystallization kinetics in both statistical and block copolymers. 

Thermoplastic perfluorocyclobutane arylene ether polymers offer a solvent soluble, melt processable, low dielectric alternative to conventional fluoropolymers. Relatively little time has been spent on their development, however. The bifimctional monomers have proven quite useful as comonomers in modifying the thermal and mechanical properties of high Tg thermoset copolymers. In particular, the siloxane PFCB polymer discussed earlier (Figure 3) exhibits a Tg = 16 C (DSC) thereby providing a reactive toughening or flexibilizing additive either as block type copolymers or comonomer for random incorporation (8),... 

Comonomers can be incorporated into the growing chain at random or as groups of identical monomers, known as blocks. The polymerization catalyst and reaction conditions control... 

Comonomers, such as 3-hydroxyvalerate (3HV, ethylene R-unit (-CH2-CH3) in Fig. 1) and 4-hydroxybutyrate, have been incorporated in the PHB chains using specific additives in the growth medium of the bacteria [21-25]. It has been shown by nuclear magnetic resonance (NMR) studies that poly(3HB-co-3HV) has a statistically random distribution of the monomer units throughout a range of compositions varying from 0 to 90 mol % 3HV [23-26]. 

Despite this tremendous versatility, there is still a fundamental limitation for these random copolymers melting point and modulus (stiffness) are inextricably coupled to the density (or percentage short-chain branching from LAO comonomer) as shown in Fig. 1. The same method employed to lower modulus (incorporation of comonomer) results in a thinning of the polyethylene crystals, concomitant with a lowering of the melting point, according to a relationship established by Flory [8],... 

The level of short-chain (SCB) and long-chain (LCB) branches control the solid resin density of a PE resin. For example, the level of SCB is controlled by the amount of alpha olefin comonomer incorporated into LLDPE resin as a pendant group. The random positioning of the pendant groups disrupts the crystailization process when the polymer is cooled from the molten state, causing the level of crystallinity to decrease with increasing amounts of alpha olefin comonomer. 

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