MPEG-1 Audio Layer II (MP2) is pretty similar to MASCAM which was documented in 1988. "Low bit-rate coding of high-quality audio signals. An introduction to the MASCAM system" by G. Thiele, G. Stoll and M. Link, published in EBU Technical Review, no. 230, pp. 158-181, August 1988. Similarities include scale factors, subband coding, allocating different numbers of bits to different subbands for each sample.
The Pseudo-QMF filter bank used is very close to the Pseudo-QMF technique document in: H. J. Nussbaumer. "Pseudo-QMF Filter Bank", IBM technical disclosure bulletin., Vol 24. pp 3081-3087, November 1981
There don't seem to be any place on the internet that explicitly claims that they have patents for MP2 encoding or decoding. AudioMPEG mentions MP2, but they explicitly state that they are not licensing for Video-CD players, which use MP2.
I have not located any documentation on the MP2 synthesis window. In the MPEG-1 audio spec this is basically given as magic numbers to be used. Introduction to Digital Audio Coding and Standards lists S. Searing, "Suggested Formulas for Audio Analysis and Synthesis Windows", ISO/IEC JTC1/SC29/WG11 MPEG 91/328, November 1991 as a reference for where this comes from, but I have not been able to track down this document.