Page 178 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Polycondensation Polymers 141

The shape of the microfi ber influences the end properties. For instance, Tomen has developed

TM

Technofi ne , which is a polyester microfiber with a “W” shape cross-section. The increased sur-
face allows a more rapid transport of water away from the skin and also increases the evaporation
rate making garments made from it quicker drying and more adsorbent.
Most textiles have limited elongation but many of the microfiber textiles have elongations of

100%.

Currently, no industry regulations exist that describe the amount of microfiber that must be
present to call it a microfiber material. Even so, typically industrial use calls for a material to be at

least 35%–40% microfiber to be called a microfiber product. Microfibers are most commonly used
in dress and blouse garments. They are also used to make hosiery, ties, scarves, intimate apparel,
curtains, draperies, sheets, towels, rainware, swimwear, blankets, tents, sleeping bags, track and
jogging-wear, as well as many other items. The greater surface area results in a fabric with deeper,
richer, and brighter colors possible.

The care of microfiber products is similar to that of the normal-fiber materials made from
the same polymer. One caution is heat sensitivity. Because the fibers are so fine, heat penetrates

more quickly causing them to scorch or glaze more quickly than “normal” fibers if too much

heat is applied or heat is applied over too long a period. Typically, microfibers are wrinkle resis-
tant, but if ironing is done, then it should be accomplished using lower temperatures and only
as directed.
4.20 GENERAL STEPWISE POLYMERIZATION
From an equation, such as Equation 4.93, it is possible to derive expressions describing the molec-
ular weight distribution of stepwise polymerizations at any extent of polymerization. This relation-
ship is more easily derived from a statistical standpoint. The following statistical treatment assumes
the reaction to be independent of chain length.
We can write a general equation for the formation of a linear polymer formed from the reaction
of bifunctional reactants A and B as follows:

nA + nB → A(BA) B (4.93)
n−1
The probability of finding a repeating unit AB in the polymer is “p,” and the probability of fi nding

n−1
“n−1” of these repeat units in the polymer chain is p . Likewise, the probability of finding an unreacted

molecule of A or B is 1−p. Thus, the probability (p ) of finding a chain with n repeat units (BA) is

n n
P = (1 − p) p n–1 (4.94)
n
N is the probability of choosing (at random) a molecule with (AB) repeat units, where N is the
n n
total number of molecules and is given as follows:
N = N (1 − p) p n–1 (4.95)
n
Since

N 0 1 or N = N (1 p
−
−
N = 1 p 0 ) (4.96)

where N is the total number of structural units present, and is described by
o
2
N = N (1 − p) p n–1 (4.97)
n o

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