Effect of Comonomer Content

The fraction of comonomer units in the copolymer chains is the most important factor affecting chain crystallizability and, therefore, crystallization temperature. This is due to the fact that comonomers act as chain defects, interrupting chain regularity and greatly lowering chain crystallizability. 

Sarzotti et al. [58] investigated the effect of comonomer content on Crystaf profiles using a series of ethylene/l-hexene copolymers with different comonomer contents but approximately the same molecular weight, effectively eliminating any possible misinterpretations that might arise because of molecular weight effects (Fig. 34) [58]. As expected, Crystaf peak temperatures are dramatically influenced by the CC of the copolymer chains. Moreover, the Crystaf profiles become broader with an increase in comonomer content. 

The decrease in Crystaf peak temperature can be simply explained with Eq. 4, as the chain composition alters the thermodynamic interaction parameter for the copolymer, xi- To understand the broadening of the distribution. 

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Fig. 5 Effect of comonomer content on the coalescence behavior of polyethylene copolymers at ramped temperature (111-226.5°C at ll°C/min). The relative methyl content for PE9-0, PEIO-O, and PEI 1-0 is 0.95, 0.56, and 0.15, respectively. (Erom RQfP )...

PEC, PPO, and PS are amorphous materials as normally melt processed, a fact which prevents the use of melting point depression analyses for experimentally determining AHnix or B for the blends with PS. Isotactic polystyrene, i-PS, is able to crystallize, is miscible with PPO, and has been successfully used to determine the parameters related to AHaix (7,12.18). This study shows that i-PS is also miscible with PEC copolymers which contain up to 20 moleX trimethyl comonomer. This fact permits the use of i-PS melting point depression analysis to determine the effect of comonomer content on AHaix with i-PS. 

The development of the concepts of run number, average sequence lengths and triad distributions would be of little more than academic interest if they could not be usefully applied. The concept of run number is most valuable in a consideration of the effect of comonomer content versus branch length in affecting polyethylene density. The following section utilizes the run number in a correlation with a number of polyethylene physical properties. 

Fig. 34 Effect of comonomer content on Crystaf profiles. These samples are ethylene/ 1-hexene copolymers synthesized using a single-site-type catalyst. All samples have similar molecular weights [58]...

The present study first examines the effect of comonomer content on the miscibility of random EO copolymers. The study is extended to test the miscibility of random EOs with OBCs of about the same molecular weight. The effect of blocky chain structure on the miscibility is discussed. The interaction parameter % for the blends of two random EO copolymers is calculated and tested for the copolymer equation. 

The subject of the crystallization of copolymers can be quite complex, dependent on the comonomer. It should also be recognized that the effects of variations in tacticity are very similar to the effects of comonomer inclusion, since both are effectively the insertion of defects into the polymer chain. The earliest treatment [26] recognized this fact, and is applicable to any defect, whether tactic, head-to-head link or comonomer, when measured as a defect content. This approach makes the assumption that all defects are excluded from the crystal. On this basis the probability of forming a critical secondary nucleus is dependent on the distribution of the defects throughout the polymer chain. The formulation of the probabilities leads to the logarithm of the rate of linear growth of a spherulite being dependent on the defect concentration. In practice, the behavior of most copolymers... 

Polymeric films have been prepared under UV radiation of urethane acrylate combined with functional monomers used as reactive diluents. Amount of photoinitiator (Irgacure 184) and radiation does intensity were optimized UV-cured films were characterized by film hardness, gel content, and tensile properties these properties were correlated with glass transition temperatures (Tg) of the polymer films. The Tg of the film was caleulated by using the Fox equation. Effect of comonomer diluents on these properties also was investigated in light of the changed Tg values of the polymeric films prepared in he presence of co-diluent. 

The effect of comonomer type was studied by Brull et al. [59] using propylene/1-olefin copolymers with several comonomer types (1-octene, 1-decene, 1-tetradecene, and 1-octadecene). They reported that, for their set of samples, not only Crystaf peak temperatures but also melting and crystallization temperatures measured by DSC were independent of comonomer type but depended strongly on comonomer content. 

Blends of isotactic propylene-co-ethylene (EP, 3-4.6 mol% ethylene) and propylene-co-l-butene (BP, 7.6 mol% 1-butene) random copolymers were studied by Bartczak et al. [66,67]. The authors investigated the effect of type, content, and distribution of comonomer units on the miscibility of the components, the crystallization behavior, morphology, and thermal and mechanical properties. 

Hydrolysis of amide groups to carboxylate is a major cause of instability in acrylamide-based polymers, especially at alkaline pH and high temperatures. The performance of oil-recovery polymers may be adversely affected by excessive hydrolysis, which can promote precipitation from sea water solution. This work has studied the effects of the sodium salts of acrylic acid and AMPS, 2-acrylamido-2-methylpropanesulfonic acid, as comonomers, on the rate of hydrolysis of polyacrylamides in alkaline solution at high temperatures. Copolymers were prepared containing from 0-53 mole % of the anionic comonomers, and hydrolyzed in aqueous solution at pH 8.5 at 90°C, 108°C and 120°C. The extent of hydrolysis was measured by a conductometric method, analyzing for the total carboxylate content. 

Copolymers of NIPAAM with acrylamide (AAM), N-methyl acrylamide (NMAAM) and N-ethyl acrylamide (NEAAM) exhibited LCSTs elevated in proportion to their comonomer content. As expected acrylamide was the most effective at elevating the LCST of the copolymer formed. However, NEAAM was more effective than NMAAM. 

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