
TY  - JOUR
A1  - Fallon, GD 
A1  - Holland, KA 
A1  - Rae, ID 
T1  - Thermal-Degradation of Polymers and Polymer Models. V. A Model for Copoly(styrene-methyl methacrylate)
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1990
VL  - 43
IS  - 3
SP  - 521
EP  - 533
KW  - 
UR  - https://doi.org/10.1071/CH9900521 
N2  - The synthesis of (±)- and meso-dimethyl 2,3-dimethyl-2,3-bis(2&#8242;-methyl-2&#8242;-phenylpropyl)butane-dioate from methyl 2,4-dimethyl-4-phenylpentanoate , via a silyl  enol  acetal, is described. The X-ray structure of the meso isomer shows serious distortions from normal bond lengths and angles, most notably a length of 162.7(4) pm for the crowded central C-C bond. The compounds were synthesized as models for head-to-head units which might form by chain termination through dimerization of macroradicals during copolymerization of styrene and methyl methacrylate . Thermal degradation of the diphenyl -substituted diesters at 210&#176; gave products which may have formed by plausible routes from radicals resulting from homolytic cleavage of the crowded C-C bond. Inclusion of the phenyl groups makes the molecules more crowded than the corresponding tetraesters which were reported earlier, and a comparative rate study shows that the aromatic compounds are less stable to heat as a result of the penultimate effects of greater crowding at carbons which are &#946; to the thermally vulnerable bond. 
ER  -

