Controlled Molecular Weight Condensation Polymers

Macromolecular monomers, called macromonomers or macromers, are a relatively new category of functionalized polymer materials having a molecular weight range of 10 -10 and possessing one or more reactive polymerizable end groups [81] of those described in Table 3.2. The 

Rudin A. The Elements of Polymer Science and Engineering. 2nd ed. San Diego Academic Press 1999. p 175. 

Flory PJ. Principles of Polymer Chemistry. Ithaca, NY Cornell University Press 1953. p 91. 

Hualun C, Xiuju Z, Kai X, Huan L, Jiangxun S, Xin L, Zien F, Ying G, Mingcai C. Polym Adv Technol 2012 23 765. 

Odian G. Principles of Polymerization. New York, NY John Wiley Sons 1991. p 54. 

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When the full distribution is needed, it is measured by size-exclusion chromatography (also called gel permeation chromatography). This is a solution technique that requires dissolution of the polymer in a reasonable solvent such as tetrahydrofuran or tetrachlorlobenzene. For polymers that require exotic solvents or solution temperatures above about 150°C, a simple measurement of solution viscosity can be a useful surrogate for the actual molecular weight. The viscosity of the pure polymer (i.e., a polymer melt viscosity) can also be used. Such simplified techniques are often satisfactory for routine quality control, particularly for condensation polymers such as PET that vary in average molecular weight but usually have a polydispersity of 2. 

Poly(dioxaboralane)s (82) (Fig. 51) with controllable molecular weights were reported to be readily obtained through the condensation reaction between 9,9-dihexylflourene-2,7- diboronic acid and pentaerythritol in toluene with an associated azeotropic removal of water. The molecular weights of the resulting polymers, which ranged between 10,000 and 76,900, were found to depend on the processing conditions of the polymers.117... 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cyclized rubber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenolic structure renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxylic acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubility is controlled by chemical and polarity differences rather than molecular size. 

The process for preparing linear poly-p-xylylenes by pyrolytic polymerization of di-p-xylylenes has been extended to include the formation of p-xylylene copolymers. Pyrolysis of mono-substituted di-p-xylylenes or of mixtures of substituted di-p-xylylenes results in formation of two or more p-xylylene species. Copolymerization is effected by deposition polymerization on surfaces at a temperature below the threshold condensation temperature of at least two of the reactive intermediates. Random copolymers are produced. Molecular weight of polymers produced by this process can be controlled by deposition temperature and by addition of mercaptans. Unique capabilities of vapor deposition polymerization include the encapsulation of particulate materials, the ability to replicate very fine structural details, and the ability of the monomers to penetrate crevices and deposit polymer in otherwise difficultly accessible structural configurations. 

An example of the type of condensation polymers which could be synthesized is the polyester condensation polymer of controlled molecular weight and terminal functionality illustrated in the following equation (10) ... 

Highly branched and saturated oily Guerbet polymers having primary alcohols have been prepared by condensing 1,9-, 1,10-, or 1,12-aliphatic diols with behenyl alcohol and zinc oxide. To control the molecular weight, each polymer was capped with a C12 or higher fatty alcohol. 

There are two important methods for PLA synthesis direct polycondensation of lactic acid and ROP of lactic acid cyclic dimer, known as lactide. In direct condensation, solvent is used and higher reaction times are required. The resulting polymer is a material of low to intermediate molecular weight. ROP of the lactide needs catalyst but results in PLA with controlled molecular weight. Depending on the monomer and reaction conditions, it is possible to control the ratio and sequence of d- and L-lactic add units in the final polymer [74,75],... 

These two approaches, condensation and ring opening polymerization, have been developed by many workers through the years to the point that a wide variety of polymers and copolymers with controlled molecular weight, molecular weight distribution, and chemical composition are now available in both linear and branched forms with a variety of end group chemistries. 

Miyakoshi, R., Yokoyama, A., and Yokozawa, T. (2008a) Development of catalyst-transfer condensation polymerization. Synthesis of 7t-conjugated polymers with controlled molecular weight and low polydispersity. Journal of Polymer Science Part A-Polymer Chemistry, 46,753-765. 

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